1. Field of the Invention
The present invention relates to an indium-substituted aluminate phosphor and a method for making the same or more precisely, an aluminate-based phosphor whose aluminum element is partially substituted with indium and a method for making the phosphor.
2. Description of the Background
Luminescent substances such as fluorescent pigments and phosphors emit visible light when they are stimulated by the absorption of UV radiation, visible light or both. While fluorescent substances cease to emit the light immediately after the stimulus is removed, phosphors continue to emit the light for a considerable period after the stimulus is removed. This characteristic of phosphors is called phosphorescence, and because of this characteristic, phosphors are widely used in luminous clocks, watches, evacuation signs, traffic safety signs and indoor displays of various kinds.
Recently, aluminate-based phosphors such as SrAl.sub.2 O.sub.4 : Eu, Dy and silicate-based phosphors such as Sr.sub.2 MgSi.sub.2 O.sub.7 : Eu, Dy have been developed. These phosphors have solved many shortcomings of the conventional sulfide-based phosphors; however, their luminance and afterglow characteristics need further improvement.
An aluminate phosphor is disclosed in U.S. Pat. No. 5,376,303 (hereinafter referred to as the '303 patent) under the title "Long Decay Phosphors". This phosphor is comprised of rare-earth metal activated, divalent, boron-substituted aluminates.
Another aluminate phosphor is disclosed in U.S. Pat. No. 5,424,006 (hereinafter referred to as the '006 patent) under the title "Phosphorescent Phosphor". This phosphor is activated by europium and is comprised of aluminate and at least one metal element selected from calcium, strontium and barium.
Yet another aluminate phosphor is disclosed in U.S. Pat. No. 5,686,022 (hereinafter referred to as the '022 patent) under the title "Phosphorescent Phosphor". This phosphor has a composition similar to the phosphor disclosed in the '006 patent but differs in the ratio of the metal constituent, M, and the oxygen constituent, O.
The contents of these patents are incorporated herein by reference in their entirety.